Syphilis is a sexually transmitted infection caused by the spirochete bacterium treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis. Other human diseases caused by related treponema pallidum include yaws (subspecies pertenue), pinta (subspecies carateum), and bejel (subspecies endemicum).
The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and tertiary). The primary stage classically presents with a single chancre (a firm, painless, non-itchy skin ulceration), secondary syphilis with a diffuse rash which frequently involves the palms of the hands and soles of the feet, latent syphilis with little to no symptoms, and tertiary syphilis with gummas, neurological, or cardiac symptoms. It has, however, been known as “the great imitator” due to its frequent atypical presentations. Diagnosis is usually via blood tests; however, the bacteria can also be detected using dark field microscopy. Syphilis can be effectively treated with antibiotics, specifically the preferred intramuscular penicillin G (given intravenously for neurosyphilis), or else ceftriaxone, and in those who have a severe penicillin allergy, oral doxycycline, or azithromycin.
Syphilis is believed to have infected 12 million people worldwide in 1999, with greater than 90% of cases in the developing world. After decreasing dramatically since the widespread availability of penicillin in the 1940s, rates of infection have increased since the turn of the millennium in many countries, often in combination with human immunodeficiency virus (HIV). This has been attributed partly to unsafe sexual practices among men who have sex with men, increased promiscuity, prostitution, and decreasing use of barrier protection.
As set forth above, diagnosis of syphilis is usually through blood tests. There are presently two types of serological tests used for the diagnosis and treatment of syphilis infection: treponemal tests, which utilize antigens prepared from the causative agent treponema pallidum, and non-treponemal tests, which employ antigens not derived directly from the causative agent.
The Centers for Disease Control (CDC), Atlanta, Ga., recommends that syphilis screening, and the assessment of treatment, be performed first using non-treponemal tests because it is believed that non-treponemal tests are more sensitive. In such tests, a false positive is possible. The CDC further recommends that positive screening test results be confirmed with a treponemal test. It is noted that the non-treponemal tests can be used for monitoring post-treatment and for detection of re-infection. There are currently two non-treponemal tests in common usage: the Venereal Disease Research Laboratory (VDRL) Test and the Rapid Plasma Reagin (RPR) Test.
The VDRL Test is a non-treponemal serological screening for syphilis used to assess response to therapy, to detect CNS involvement, and as an aid in the diagnosis of congenital syphilis. The basis of the test is that antibody (IgG, IgM or IgA), produced by a patient with syphilis, reacts with a compound comprised of cardiolipin, cholesterol, and lecithin. The test is performed by mixing the patients serum with compound described above. Positive sera result in “flocculation.” Simply put, the VDRL Test is a manual coagulation test with a qualitative, subjective, visual readout requiring the use of a microscope. More specifically, a sample of the patient's antibody is mixed in a test tube, or on a microscope slide. A clinician is required to view the test tube, or slide and determine, based upon the clinician's own experience and training, if the visual presentation indicates coagulation to an extent sufficient to call the results positive. Quantitative test results require a serial dilution of the test sample and testing of multiple dilutions. Thus, the VDRL Test is labor intensive and unable to be automated. It is known that false negatives arise in the VDRL Test due to the Prozone Effect, or “Hook” Effect, in cases of strongly positive samples.
The RPR Test is a particle agglutination test. The RPR Test also is a manual test, with a qualitative, subjective, visual readout. The RPR Test utilizes a colloidal suspension of cardiolipin, cholesterol, and lecithin, mixed with micro-particulate carbon. Thus, the RPR Test uses the same antigen as the VDRL Test, but, in the RPR Test, the antigen has been bound to a carbon particle to allow visualization of the flocculation reaction without the need of a microscope. The mixture is placed on a test area of a card and the clinician is able to read the results based upon a visually detectable clumping of the carbon particles. Like the VDRL Test, the RPR Test is a quantitative test where the results require a serial dilution of the test sample and testing of multiple dilutions. Thus, the RPR Test is labor intensive and unable to be automated. Similarly, false negatives arise due to the Prozone Effect. FIG. 1 is a photograph of a RPR Test card. The clumping of the carbon particles is shown in a positive test result on the left (circle number 9). The right test area of the card (circle number 10), in contrast, where no clumping has occurred, is indicative of a negative result.
Three components comprise the VDRL antigen: cardiolipin; cholesterol; and lecithin. These components are lipid in nature. As such, they are not soluble in aqueous solution. In the classical VDRL test, therefore, the three-component antigen complex is used as a colloidal suspension. It must be prepared under very carefully controlled conditions, just prior to performing the test. Due to its inherent lack of stability, the colloidal suspension must be prepared daily for immediate use. Because of the inherent unstable property, there is no way to preserve the mixed antigens in colloidal suspension for long periods of time. It would be beneficial to provide a sensitive and specific non-treponemal syphilis screening and assessment of treatment test, that is stable and has a long shelf life.
Neither the VDRL Test nor the RPR Test lend themselves to automation. It would be beneficial to provide a syphilis screening and assessment of treatment test that is able to be automated.
A need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.